Resolving Conflicts

# 1) When a conflict occurs
git merge feature/login
# CONFLICT (content): Merge conflict in src/auth.ts
# Automatic merge failed; fix conflicts and then commit the result.

git status
# Unmerged paths:
#   both modified:   src/auth.ts

# 2) Conflict markers — what you'll see in the file
#
# <<<<<<< HEAD                          ← your branch's version
# const TOKEN_TTL = 3600;
# =======                                ← divider
# const TOKEN_TTL = 86400;                 ← incoming version
# >>>>>>> feature/login                  ← incoming branch
#
# You decide: pick yours, pick theirs, combine both, or write something new.

# 3) Resolve manually
# Edit the file, remove ALL markers, save.
git add src/auth.ts
git status
# All conflicts fixed but you are still merging.
git commit                                  # opens editor with a default merge message

# 4) Resolve with the CLI
git checkout --ours src/auth.ts             # keep your branch's whole file
git checkout --theirs src/auth.ts           # keep incoming whole file
# Then: git add src/auth.ts && git commit

# 5) Resolve with a merge tool (3-way diff)
git mergetool                                # uses configured tool (vimdiff, meld, kdiff3, VS Code, IntelliJ)
# Configure:
git config --global merge.tool vscode
git config --global mergetool.vscode.cmd 'code --wait $MERGED'

# 6) Abort the merge — start over
git merge --abort
# Returns the working tree to the pre-merge state.

# 7) Look at the three versions
git checkout HEAD~ src/auth.ts                # COMMON ANCESTOR version (use --merge during rebase)
git show :1:src/auth.ts                       # common ancestor
git show :2:src/auth.ts                       # your version (ours)
git show :3:src/auth.ts                       # incoming (theirs)

git diff :2:src/auth.ts :3:src/auth.ts        # what changed between ours + theirs

# 8) Diff3 conflict style — shows the COMMON ANCESTOR too
git config --global merge.conflictstyle diff3
# Now markers include an extra section:
# <<<<<<< HEAD
# const TOKEN_TTL = 3600;
# ||||||| ancestor                       ← what both branches started from
# const TOKEN_TTL = 7200;
# =======
# const TOKEN_TTL = 86400;
# >>>>>>> feature/login
#
# Knowing the ancestor often makes the right choice obvious.

# 9) Conflicts during rebase
git rebase main
# Resolve, add the file, then:
git rebase --continue                         # apply the next commit
git rebase --skip                              # drop this commit and continue
git rebase --abort                             # give up, go back to where you started

# 10) Conflicts during cherry-pick
git cherry-pick abc1234
# Resolve, add file, then:
git cherry-pick --continue
git cherry-pick --skip
git cherry-pick --abort

# 11) rerere — REuse REcorded REsolution
git config --global rerere.enabled true
# Git records how you resolved a conflict; the next time the same conflict appears it auto-applies.
# Especially useful for long-running feature branches against fast-moving main.

# 12) Lockfile + generated file conflicts
# package-lock.json, pnpm-lock.yaml, yarn.lock, Cargo.lock, go.sum:
#   • Don't merge manually; regenerate after resolving package.json
#       git checkout --theirs package-lock.json
#       npm install
#       git add package-lock.json
#
# • Add to .gitattributes:
#       *.lock merge=lockfile
#   then in .git/config: [merge "lockfile"] driver = npm install   (tooling can be custom)

# 13) Binary file conflicts
git checkout --ours image.png
git checkout --theirs image.png
git add image.png
# Can't merge binary content; you must pick one or rebuild.

# 14) Preventing conflicts
# • Smaller PRs merged faster
# • Pull main into your branch daily (git pull --rebase or git merge main)
# • Split unrelated changes into separate commits
# • Refactor in a SEPARATE PR before adding features
# • Code owners + module ownership — fewer people touching the same file
# • Auto-formatters running on save — reduces noise conflicts on whitespace

# 15) Editor + IDE help
# VS Code:    'Merge Editor' shows current/incoming/result with click-to-accept
# IntelliJ:   'Resolve Conflicts' dialog; 3-way merge with semantic awareness
# GitHub:     Web editor for simple text conflicts

# 16) GitHub PR merge conflicts
# GitHub blocks merging when conflicts exist. Resolve locally:
git fetch origin
git checkout feature/login
git merge origin/main
# Resolve, push:
git push

# Or use the GitHub UI for trivial conflicts (only text-level edits).

# 17) Common bugs
# • Forgetting to remove ALL conflict markers → committing broken code
# • Choosing 'ours' when fixing a logic conflict → silently dropping the other team's work
# • Resolving lockfile conflicts manually → out-of-sync dependency tree
# • Conflict avoidance via long-lived branches → much bigger conflict later
# • Running 'git pull' on a branch with conflicts not resolved → confusing reset
# • CI green after 'theirs' resolution → tests passed but business logic dropped; READ DIFF before commit
# • Resolving rebase conflicts then forgetting --continue → state stuck in 'rebasing'
# • Reverting a merge without --mainline → fails on octopus merges; specify parent

# Edit conflicting files, look for <<<<<<<.
git add resolved-file
git commit         # if merge
git rebase --continue    # if rebase